1. Field of Invention
The present invention relates to an electro-optical device in which a conductive layer different from other conductive layers constituting scanning lines and data lines is used in a peripheral circuit to improve design versatility in the peripheral circuit, a method for making the same, and an electronic apparatus using the electro-optical device as a display section.
2. Description of Related Art
In electro-optical devices, such as in liquid crystal devices that display using liquid crystal as an electro-optical material, the liquid crystal is disposed between a pair of substrates. Among these, for example, an active-matrix liquid crystal device for driving pixel electrodes by three-terminal switching elements has the following configuration. That is, in this liquid crystal device, a plurality of scanning lines and a plurality of data lines are provided so as to cross each other on one substrate, and each of these crossings is provided with a combination of a three-terminal switching element, such as a thin film transistor (hereinafter referred to as TFT), and a pixel electrode. In this device, the TFT turns on to supply an image signal, applied to the corresponding data line, to the pixel electrode when the scanning signal supplied to the scanning line corresponding to the crossing is an active level. The other substrate is provided with transparent counter electrode which opposes the pixel electrodes.
Driving circuits which drive these scanning lines and data lines generally include at least a scanning line driving circuit, a data line driving circuit, and a sampling circuit. Among these, the scanning line driving circuit supplies scanning signals at a predetermined time interval, whereas the data line driving circuit supplies sampling signals at a predetermined time interval. The sampling circuit supplies image signals supplied by a sampling switch, which is provided to each data line via an image signal line, to the corresponding data line in response to the sampling signals.
Moreover, a peripheral-circuit-built-in-type electro-optical device provided with these driving circuits in the peripheries of a region (display region) of a pixel electrode array is developed. In such an electro-optical device, active elements constituting the driving circuits and switching elements connected to the pixel electrodes are formed by a common process, in consideration of efficiency of the production process. For example, in the above liquid crystal device, elements constituting the driving circuits are TFTs which are formed by the same process as the switching elements connected to the pixel electrodes. Such peripheral-circuit-built-in-type electro-optical devices are advantageous for miniaturization and reduction in overall cost of the device, compared with electro-optical devices provided with external driving circuits.
Recently, higher definition arrays, for example, an extended graphics array (XGA: 1024xc3x97768 dots), a super extended graphics array (SXGA: 1365xc3x971024 dots), and an ultra extended graphics array (UXGA: 1600xc3x971200 dots), have been required for all displays including electro-optical devices
To achieve a higher definition array along with miniaturization of the device requires a technology to significantly reduce the array pitch of the semiconductor devices and the array pitch of the data lines. Since the scanning line driving circuit supplies scanning signals to each scanning line, a unit circuit (latch circuit) constituting a portion of the scanning line driving circuit must be contained within the array pitch between the scanning lines. Since the data line driving circuit sequentially supplies sampling signals to sampling switches provided to data lines, a unit circuit constituting a portion of the data line driving circuit must be contained within the array pitch or an integral multiple thereof. However, to achieve a higher definition array and miniaturization of the peripheral-circuit-built-in-type electro-optical device it is difficult to design the device so as to form the unit circuits in the scanning line driving circuit and the data line driving circuit within extremely limited spaces.
The present invention is completed in view of the above circumstances and has an object to provide an electro-optical device that enables improved design versatility in peripheral circuits. In order to achieve the above object, an electro-optical device according to a first aspect of the present invention comprises a plurality of scanning lines and a plurality of data lines, a combination of a switching element and a pixel electrode provided that correspond to each crossing between the scanning lines and the data lines, a conductive interlayer for electrically connecting the corresponding switching element and the corresponding pixel electrode, and a peripheral circuit containing leads which comprise the same layer as the conductive layer constituting the conductive interlayer and driving the switching element.
According to this configuration, the conductive interlayer is used for connecting each switching element and each pixel electrode in the region of the array of the pixel electrodes (the display region), and leads composed of the same conductive layer as the conductive interlayer are also used in the peripheral circuit. In other words, the conductive interlayer used in the display region is also used as parts of the leads in the peripheral circuit. Since a novel lead layer is provided in the peripheral circuit, design versatility is improved.
In this embodiment, the conductive interlayer is preferably connected to an electrode of the switching element via a first contact hole provided corresponding to the electrode, whereas the pixel electrode is connected to the switching element via a second contact hole. In this configuration, the electrode of the switching electrode is connected to the conductive interlayer via the first contact hole, whereas the pixel electrode is connected to the conductive interlayer via the second contact hole. Since the conductive interlayer functions as a barrier film when the pixel electrode is connected to the other end of the switching element, defects occurring when the contact holes have long distances can be reduced.
In this embodiment, each pixel electrode is preferably provided with a storage capacitor of which one end is connected to the pixel electrode and the other end is commonly connected, and the conductive interlayer functions as a part of an electrode constituting the storage capacitor. According to this configuration, the retention of the voltage in the pixel electrode is improved by the storage capacitor in which the conductive interlayer functions as a part of an electrode constituting the storage capacitor.
In this embodiment, the conductive interlayer may have a light-shading effect, part of the light which pass through or is reflected by the pixel electrodes being regulated by the conductive interlayers. According to this configuration, an exclusive shading film can be omitted at least in the region defined by the conductive interlayer among the light transmission or reflection regions. Thus, the configuration can be simplified.
For achieving the above object, an electro-optical device in accordance with a second aspect of the present invention comprises first, second, and third conductive layers, formed in that order, the third conductive layer having resistance which is lower than that of the first conductive layer, a plurality of scanning lines comprising the first conductive layer, a plurality of data lines comprising the third conductive layer and formed so as to cross the plurality of scanning lines, a combination of a switching element and a pixel electrode provided corresponding to each crossing between the scanning lines and the data lines, a conductive interlayer for electrically connecting the switching element and the corresponding pixel electrode, and a peripheral circuit which is provided with leads comprising the first, second, and third conductive layers and drives each switching element.
According to this configuration, the conductive interlayer is used for connecting the switching element to the pixel electrode, and leads composed of the second conductive layer which is the same as the conductive interlayer are used together with the leads composed of the first conductive layer and the leads composed of the second conductive layer in the peripheral circuit. In other words, the conductive interlayer used in the display region is also used as parts of the leads in the peripheral circuit. Since a novel lead layer is provided in the peripheral circuit, design versatility is improved.
In this embodiment, the conductive interlayer is preferably connected to an electrode of the switching element via a first contact hole provided corresponding to the electrode, whereas the pixel electrode is connected to the switching element via a second contact hole. In this configuration, the electrode of the switching electrode is connected to the conductive interlayer via the first contact hole, whereas the pixel electrode is connected to the conductive interlayer via the second contact hole. Since the conductive interlayer functions as a barrier film when the pixel electrode is connected to the other end of the switching element, defects occurring when the contact holes have long distances can be reduced.
Since the third conductive layer has lower resistance than that of the first conductive layer, it is preferable that all the leads be formed of the third conductive layer. Since crossings and branches of leads are inevitably present in the peripheral circuit, it is impossible that all the leads are formed of the third conductive layer. Thus, in this aspect, the peripheral circuit has a configuration including a parallel lead in which a lead comprising the first conductive layer and a lead comprising the second conductive layer are electrically connected, when, for example, leads are composed of the first conductive layer having high resistance. By using the parallel lead in which the lead composed of the first conductive layer and the lead composed of the second conductive layer are electrically connected, the wiring resistance thereof can be reduced compared to the use of the first or second conductive layer alone.
Such a parallel lead may be used at a portion in which a branched lead is branched from a line comprising the third conductive layer and is used in intersections with other leads different from the lead comprising the third conductive layer. Although such a branched lead should be composed of the third conductive layer having low resistance, a portion composed of the third conductive layer and crossing the other lead cannot be formed of the same third conductive layer.
When the peripheral circuit includes h image signal lines for supplying image signals in response to h data lines wherein h is an integer of at least 2, and sampling switches, each provided to the corresponding data line, samples the corresponding image signal among the image signals supplied to the h image signal lines in response to a predetermined sampling signal, and supplies the image signal to the corresponding data line, the parallel leads are used as at least parts of lines which are branched from the image signal lines towards the sampling switches. Since such leads supply image signals to the pixel electrodes, these leads must be composed of the third conductive layer having low resistance. However, these leads cannot be formed of the same third conductive layer because the leads cross the other image signal lines.
When the parallel lead is formed in this aspect, the lead comprising the second conductive layer of the parallel lead may pass through between third and fourth contact holes which expose the lead comprising the first conductive layer, and the lead comprising the third conductive layer of the parallel lead is provided a position corresponding to the third or fourth contact hole and is electrically connected to a fifth contact hole which exposes the lead comprising the second conductive layer (first configuration). Alternatively, the lead comprising the second conductive layer of the parallel lead may pass through between third and fourth contact holes which expose the lead comprising the first conductive layer, and the lead comprising the third conductive layer of the parallel lead is provided a position different from the third and fourth contact holes and is electrically connected to a sixth contact hole which exposes the lead comprising the first conductive layer (second configuration). When a stress due to warp is applied to the second conductive layer, cracks may be formed during providing a contact hole which exposes the lead comprising the second conductive layer. Since no contact hole exposing the second conductive layer is provided in the second configuration, defects due to the formation of the cracks can be reduced.
In the first and second configurations, the lead comprising the second conductive layer of the parallel lead is preferably provided between the third and fourth contact holes and is connected to the lead comprising the first conductive layer in one contact hole or a plurality of contact holes. The parallel lead is also connected in parallel in the contact hole(s) other than the third and fourth contact holes.
In this aspect, the peripheral circuit may comprise leads comprising the first, second, and third conductive layers in a partial portion thereof. According to this configuration, three different layer leads are arranged in the same region, reducing the space.
In this embodiment, each pixel electrode is preferably provided with a storage capacitor of which one end is connected to the pixel electrode and the other end is commonly connected, and the conductive interlayer functions as a part of an electrode constituting the storage capacitor. According to this configuration, the retention of the voltage in the pixel electrode is improved by the storage capacitor in which the conductive interlayer functions as a part of an electrode constituting the storage capacitor.
Preferably, the storage capacitor includes a first capacitor comprising the electrode of the switching element, the capacitor line composed of the second conductive layer, and a gate oxide film of the switching element provided therebetween, and a second capacitor comprising the conductive interlayer, the capacitor line, and an insulating interlayer provided therebetween. Since the storage capacitor includes the first capacitor and the second capacitor, capacitance is increased compared to a single capacitor configuration.
In this embodiment, the first conductive layer preferably comprises polysilicon. When the scanning lines are formed of a metallic thin film or metal silicide, defects such as separation will occur in a subsequent high-temperature process.
In this embodiment, the third conductive layer preferably comprises aluminum. By this configuration, resistance of the third conductive layer can be easy to be reduced.
Furthermore, in this embodiment, the second conductive layer preferably comprises a material having a melting point which is higher than that of a material constituting the third conductive layer, since melting or separation in the high-temperature process after the formation of the second conductive layer must be prevented. Examples of the materials having high melting points include polysilicon, titanium (Ti), chromium (Cr), tungsten (W), tantalum (Ta), molybdenum (Mo), lead (Pb), and alloys and metal silicides thereof.
An electro-optical device in accordance with a third aspect of the present invention comprises a plurality of scanning lines and a plurality of data lines, a combination of a switching element and a pixel electrode provided corresponding to each crossing between the scanning lines and the data lines, a conductive interlayer for electrically connecting the switching element and the corresponding pixel electrode, a peripheral circuit for driving the switching element, and leads connected to the peripheral circuit and comprising the same layer as a conductive layer which constitutes the conductive interlayer.
In this aspect, the leads connected to the peripheral circuit can be formed of the same conductive layer as the conductive interlayer used for connecting the switching element and the pixel element. Since this conductive layer can as a novel lead layer, design versatility is improved.
In this embodiment, the leads cross beneath at least one image signal line which comprises the same layer as a conductive layer which constitutes the data lines. In this configuration, the leads crossing the image signal lines can be formed of the same conductive layer as the conductive interlayer.
A plurality of image signal lines are provided, each image signal line is connected to the corresponding lead, and these leads have substantially the same size. In this configuration, the leads connected to these image signal lines have substantially the same resistance, differences between image signals due to the difference in resistance between the leads can be prevented, ensuring satisfactory display.
In this embodiment, the electro-optical device can further include a first conductive layer which comprises the same layer as the conductive layer constituting the data lines, a second conductive layer which comprises the same layer as the conductive layer constituting the data lines and is formed at a position distant from the first conductive layer, and a third conductive layer which comprises the same layer as the second conductive layer of the switching element, the third conductive layer being electrically connected with the first conductive layer and the second conductive layer via a contact holes. According to this configuration, the third conductive layer comprising the same layer as the semiconductor layer of the switching element is formed as a bypass.
In this embodiment, each lead is electrically connected to the third conductive layer via at least one contact hole. Since the lead and the third conductive layer are connected to each other in parallel in this configuration, the lead has low resistance.
This embodiment can be characterized in that the third conductive layer comprises polysilicon. According to this configuration, the lead is electrically connected to the third conductive layer of polysilicon via the contact hole. Thus, the lead does not have cracks when the lead is formed of a high-melting-point metal. Since the third conductive layer is formed of polysilicon, cracks are not formed in the polysilicon, although the third conductive layer is electrically connected to the first conductive layer and the second conductive layer via the contact hole.
This embodiment can further be characterized in that each lead is electrically connected to the third conductive layer via at least three contact holes. According to this configuration, a redundant lead is formed between the lead and the third conductive layer, preventing short-circuiting between the lead and the third conductive layer due to cracks in the lead and the third conductive layer.
This embodiment can be characterized in that an image signal line which comprises the same layer as the conductive layer constituting the data lines is arranged between the first conductive layer and the second conductive layer. According to this configuration, the image signal line comprising the same layer as the conductive layer constituting the data lines is arranged without interference the first and second conductive layers.
Since an electronic apparatus of the present invention is provided with the above electro-optical device, the design versatility of the peripheral circuit can be improved.
In accordance with the present invention, a method for making an electro-optical device having a plurality of scanning lines, a plurality of data lines, and a combination of a switching element and a pixel electrode provided at a position corresponding to each crossing between the scanning lines and the data lines, includes the steps of forming the switching element at the position corresponding to each crossing between the scanning lines and the data lines, forming a conductive interlayer connected to the switching element and a lead used in a peripheral circuit for driving the switching element using the same conductive layer, and forming the pixel electrode connected to the conductive interlayer. According to this method, a novel lead layer is provided in the peripheral circuit as in the first aspect, and thus the design versatility is increased.
In accordance with the present invention, a method for making an electro-optical device having a plurality of scanning lines, a plurality of data lines, and a combination of a switching element and a pixel electrode provided at a position corresponding to each crossing between the scanning lines and the data lines, includes the steps of: after forming the scanning lines and leads used in a peripheral circuit for driving the corresponding switching element by using the first conductive layer, and forming the switching element at the positions corresponding to each crossing between the scanning lines and the data lines, forming a conductive interlayer connected to each switching element and leads used in a peripheral circuit for driving the corresponding switching element by using a second conductive layer, forming leads used in the data lines and the peripheral circuit by using a third conductive layer and forming the pixel electrode connected to the conductive interlayer. According to this method, a novel lead layer is provided in the peripheral circuit as in the second aspect, improving the design versatility.